Add uppercase PROXY variables. Curl was failing to connect to GitHub

The machine where we were trying to install AiaB only had configure the
lowercase values for the proxy and the installation process was failing
with the following error:
```
sudo mv config.yaml /etc/rancher/rke2/
curl -sfL https://get.rke2.io | sudo INSTALL_RKE2_VERSION=v1.23.4+rke2r1 sh -
[INFO]  using v1.23.4+rke2r1 as release
[INFO]  downloading checksums at https://github.com/rancher/rke2/releases/download/v1.23.4+rke2r1/sha256sum-amd64.txt
curl: (7) Failed to connect to github.com port 443: Connection timed out
Makefile:232: recipe for target '/home/ubuntu/aether-in-a-box//build/milestones/k8s-ready' failed
make: *** [/home/ubuntu/aether-in-a-box//build/milestones/k8s-ready] Error 7
```
As soon as I added the uppercase PROXY variables, it worked fine. Here is
the link to the curl documentation about the PROXY (https://man7.org/linux/man-pages/man1/curl.1.html#ENVIRONMENT)

Change-Id: I0fa0a6bf6dcb526cacae15598a11a3eab247bf68
1 file changed